Physiologic changes during normal pregnancy

Investigators in the past year have turned their efforts to several age-old obstetric questions. Using modern experimental tools, questions were raised about the validity of N?gele's rule of 280 days as a mean gestational length. One large study agreed with the 280-day mean length, while two other studies disputed it. Current guidelines for appropriate weight gain in pregnancy range from 9 to 14 kg. Several studies found that mean weight gain in healthy pregnant women was greater than these guidelines, with a mean of 15 kg and a normal range from 8 to 25 kg. Women who exercise strenuously throughout gestation were found to have smaller babies than control subjects, with a very mild asymmetric growth retardation. Their labors came on earlier, were shorter in duration, and involved less obstetric and surgical intervention. In an interesting study of maternal hemodynamics, standing was found to be associated with a decrease of more than 15% in cardiac output compared with output in the lateral supine position in the third trimester. Investigators studied exercise in the water and found it to have less effect on fetal cardiovascular parameters than exercise of similar intensity on land.     

Immunological reactivity of maternal lymphocytes during normal pregnancy in the rat

Thoracic duct lymphocytes from pregnant PVG rats differed markedly from similar cells collected from non-pregnant donors in their reactivity in popliteal lymph node assays performed in (PVG × DA) F₁ hybrid hosts. Cells from pregnant rats failed to evoke an increase in popliteal node size commensurate with higher challenge doses of lymphocytes. This modification in maternal lymphocyte reactivity was not dependent on the presence of foetuses genetically compatible with the F₁ hybrid rats used in the popliteal lymph node assay. The mechanism responsible for the decrease in size of responding F₁ hybrid popliteal lymph nodes appeared to be based on a reduced capacity of lymphocytes from pregnant donors to stimulate a response by host lymphocytes.     

Biochemical changes of normal pregnancy and puerperium in Lagos, Nigeria.

A cross-sectional study is presented of biochemical changes in the third trimester of normal pregnancy and puerperium during the wet season in the tropical climate of Lagos, Nigeria. These changes are less marked in first than in subsequent pregnancies, and although qualitatively similar, in some respects they differ from those observed in the temperate climatic zone. The indications are that quantitative differences may exist which could be relevant to the management of pregnancy in the tropics.     

Immunological responsiveness of maternal and foetal lymphocytes during normal pregnancy in the ewe

Peripheral blood lymphocytes collected from ewes before and during pregnancy manifested constant reactivity to concanavalin A and to paternal and third party peripheral blood lymphocytes. However, in some instances, the reactivity of these maternal cells against lipopolysaccharide and lymphatic lymphocytes from paternal, foetal and third-party donors increased markedly during pregnancy. Apart from an indication that plasma from some pregnant ewes acquired the capacity to depress lymphocyte reactivity non-specifically, no evidence was obtained to suggest that maternal lymphocyte reactivity observed in vitro did not accurately reflect the capacity of these cells in the donor ewe. In particular, there was no indication that populations of maternal peripheral blood lymphocytes returning from the gravid uterus had undergone any modification of reactivity against foetal determinants.     

Structural changes and variations of uric acid in normal pregnancy

Fifteen normal pregnant women were studied. Serial measurements of serum total, free and bound uric acid and their clearances were done in early (10-20 weeks), mid- (20-30 weeks) and advanced (30-40 weeks) pregnancy, and after delivery (4-5 weeks). The following was observed. 1. A decrease in early and mid-pregnancy of total and free uric acid (p less than 0.001). 2. A gradual increase from the early to advanced pregnancy of bound uric acid (p less than 0.001). 3. An increase in early and mid-pregnancy of total uric acid clearance and a similar but more pronounced increase of free uric acid clearance (p less than 0.001). These findings explain many differences in previous conflicting reports concerning the metabolic behavior of uric acid, and place future investigation thereof on a more promising basis in normal and abnormal pregnancy.     

Placento-thyroidal relationship in normal pregnancy.

Estimations of serum HCT, HTSH, T4, T3, PBI, ETR, Triosorb, TBG-binding capacity, BMR and urinary total estrogen were made simultaneously in 160 women in normal pregnancy. TRH stimulation tests were made in 20 cases in each trimester of pregnancy. HCT was detectable even in early pregnancy, tending to increase gradually toward the terminal stage of pregnancy as serum thyrotrophin bioactivity showed. On the other hand, serum TSH level measured by radio-immunoassay remained essentially the same throughout the course of pregnancy as in the nonpregnant state, moreover, it was suggested by the TRH stimulation test that pituitary TSH secreting function of pregnant women was similar to that of the non-pregnant. These findings suggest that thyroid hyperfunction during pregnancy which is shown by progressively increased T3, T4, and PBI may not be due to high estrogen-high TBG binding capacity-low free thyroxinenegative feed back-high TSH secretion but to HCT originating from placenta. In spite of thyroid hormone increase, it is true that the clinical picture of hyperthyroidism is not manifest among normal pregnant women, and ETR remained within the non-pregnant range throughout the course of pregnancy. We have also demonstrated that Triosorb decreased progressively. This may be interpreted to be due to the increase of TBG binding capacity which is increased progressively and binds more of free thyroxine during pregnancy. Such a change in TBG binding capacity is well known to be caused by the effect of estrogen which is progressively increased during pregnancy. In a word, it is possible to say that there is a placento-thyroidal system in pregnancy; HCT elevates thyroid function and TBG increased by estrogen carries thyroid hormone to target organ.     

Serum oestriol in normal pregnancy.

Serial measurements of serum oestriol (E3) were made in 56 normal pregnancies from 10 to 40 weeks gestation using a radioreceptor assay. Several parameters of the assay and its intrapatient variability were examined. The mean curve for pregnancy E3 levels and limits of normal variation have been identified and compared with those of other series. A positive correlation was found to exist between infant birth weight and the last E3 value in normal pregnancies prior to the onset of labour. Advantages of serum E3 assays over urinary E3 determinations are discussed.     

Immunological determination of alpha-fetoproteins in pregnancy

In 53 normal pregnant women the alphafetoprotein value (AFP) was determined by two parallel methods: immunological and radioimmunological. The results of this comparative analysis have shown a high significance, the coefficient o the linear correlation r being 1.0002 and the level of agreement obtained by the t test amounting to P less than 0.01. The use of the AFP test in the course of pregnancy depends on the stage of pregnancy. In the first trimester the AFP test is useful as a test for the early detection of fetal disorders. In the second trimester the test is important for the detection of the already existing disorders of the fetus in the course of gravidity and also for the follow-up of the fetal condition. In the third trimester the AFP test could be used for the assessment of gestation age, for the prediction of the death of the fetus, and for the detection of some fetal distress. The AFP level in the mother's blood can provide information about the condition of the fetus within the feto-placental unit.     

Ritodrine hydrochloride induced cardiopulmonary and placental hemodynamic changes in normal and hypertensive late pregnancy.

Cardiopulmonary parameters (minute volume, heart rate, stroke volume, right heart, pulmonary and left heart blood volumes), blood pressure and placental blood flow were evaluated in 20 normal patients, nine patients with preeclamptic disease and 12 with essential hypertension in late pregnancy before and 60 minutes after a single i.m. dose of 10 mg of ritodrine hydrochloride. The drug caused a statistically significant increase in heart rate in all the patient groups, while the systolic and diastolic blood pressures were only slightly affected. Minute volume was unchanged in the group of normal patients, but in both hypertensive groups there was a significant increase. The placental perfusion index was statistically nearly significantly decreased in the group of uncomplicated pregnancies, statistically significantly increased in preeclamptic patients, and not affected in the group with essential hypertension. Ritodrine hydrochloride medication can be expected to have a positive effect on placental blood flow only in preeclamptic disease, and then probably in the milder forms of the disease.     

Connective tissue changes in the cervix during normal pregnancy and pregnancy complicated by cervical incompetence

When postpartum cervical biopsy specimens were compared with biopsy specimens from nonpregnant women, they revealed a 12-fold decrease in mechanical strength, a 50% reduction in the concentrations of collagen and sulfated glycosaminoglycans, a 35% reduction in hyaluronic acid, an increase in collagen extractability, and a fivefold increase in collagenolytic activity. Primiparas with relatively high concentrations of collagen and hyaluronic acid had relatively long cervical dilatation times during established labor, suggesting a physiologic importance to these variables. This correlation was not found in multiparas, even though the mean values of the biochemical parameters tested were similar to those in primiparas. Second-trimester biopsy specimens taken from patients with cervical incompetence contained normal collagen concentrations, but relatively high collagen extractabilities and collagenolytic activities, exceeding normal postpartum values. A biopsy specimen that was tested biomechanically had a very low strength and very high extensibility. Most likely, these data reflect a high turnover of collagen in incompetent cervices, resulting in a high proportion of newly synthesized collagen with low biomechanical strength.